In the Prologue to the play, just before Act 1, the Chorus foreshadows Romeo and Juliet's eventual deaths, and describes an ironic end to the plot to come:
Two households, both alike in dignity
(In fair Verona, where we lay our scene),
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
From forth the fatal loins of these two foes
A pair of star-crossed lovers take their life;
Whose misadventured piteous overthrows
Doth with their death bury their parents’ strife.
The Chorus serves a clear narrative function: its dialogue (which appears in the Prologue and at the beginning of Act 2) helps to set up and explain the plot, and it also establishes the play's tone. The Chorus's introduction in the Prologue is a rather heavy-handed form of foreshadowing that lays out a road map for the entire play. Though the "star-crossed lovers" aren't named—nor are the warring "households"—as the play's action unfolds, it becomes clear that Romeo and Juliet will die by suicide. As a result, the Prologue becomes a kind of prophecy, guiding the plot and creating suspense, as the audience anticipates the events to come.
The Chorus also clarifies one of the fundamental situational ironies of Romeo and Juliet. Though Romeo and Juliet will die, bringing unending grief to both families (who must grapple with the loss of the children they formerly neglected and oppressed), "their parents' strife" will simultaneously die and be ended forever. Thus, Romeo and Juliet's deaths serve as a kind of sacrifice, ensuring peace in Verona. Though the end of the play is undoubtedly tragic, this aspect of the conclusion offers some consolation to the audience, suggesting that even powerful rifts can be healed, and that the injustices of the past are not bound to recur in perpetuity.
In Act 4, Scene 1, Juliet—having learned that her family is about to marry her to Paris—goes to Friar Laurence and threatens to kill herself. Friar Laurence begs her not to and hastily devises a solution, which he persuades her to agree to through the use of logos:
Hold, daughter, I do spy a kind of hope,
Which craves as desperate an execution
As that is desperate which we would prevent.
If, rather than to marry County Paris,
Thou hast the strength of will to slay thyself,
Then is it likely thou wilt undertake
A thing like death to chide away this shame,
That cop’st with death himself to ’scape from it;
And if thou darest, I’ll give thee remedy.
Friar Laurence recognizes that Juliet is desperate to avoid marrying Paris; his kindness and commitment to pacifism make him sympathetic to the young lovers' plight. Moreover, since Friar Laurence has married Romeo and Juliet in secret, he knows that Juliet's marriage to Paris would not be valid—adding further complications to an already dire situation.
Friar Laurence seems to understand that ordering Juliet not to kill herself would be fruitless. She is overcome with fear and grief, and has already rebelled against instructions from the other adults in her life (namely, her parents and her Nurse, who have all encouraged her to marry Paris). Thus, he employs logos to try to reason with her, making use of her unstable mental state. If Juliet has the "strength of will" to kill herself, he reasons, then she will also have the strength to take a sleeping potion and experience a kind of temporary death by falling into a deep sleep. Then, upon waking, Friar Laurence will lead her to Romeo in Mantua. Additionally, by framing the plan as something Juliet will agree to only if she "darest," Friar Laurence is subtly taking advantage of Juliet's desperation—challenging her to prove both her love for Romeo and her own courage to rebel.
Friar Laurence's use of logical reasoning stands in opposition to Juliet's hysteria and panic. He seems to be in control of the situation, and Juliet puts her trust in him to follow along with the plan. Ironically, however, Friar Laurence's plot goes awry (when an expected message to Romeo informing him about Juliet's "death" does not arrive in time), emphasizing a major theme of the play: adults are no less fallible than children, despite their apparent wisdom. Ultimately, Friar Laurence's logical reasoning is rendered futile. In taking the potion, Juliet briefly experiences "a thing like death," just like Friar Laurence promised—but then she actually dies by suicide.